A comparator (also referred as ‘a voltage comparator’) is an integrated circuit. The voltage comparator compares the magnitudes of two input voltages to determine which is higher. Which input voltage is higher is determined and indicated by an output voltage from the comparator.
As for the conventional comparators, when the conventional comparator compares the differential input voltages, the range of the input common mode voltage identified by the comparator is not rail-to-rail. That is, the range of the input common mode voltage identified by the comparator is not from the ground voltage GND to the operation voltage VDD. If the input common mode voltage tends to the ground voltage GND, the comparator with PMOS transistor differential input pair is used. To the contrary, if the input common mode voltage tends to the operation voltage VDD, the comparator with NMOS transistor differential input pair is used.